High molecular weight alkyl disulfides



Feb. 18, 1947. w. A. scHuLzE lz'rm.l 2.415,851

` I HIGH MOLECULAR WEIGHT ALKYL DISULFIDES Filed Nov. 20, 1945 Patented Feb. '18, 1947 I man MoLsouLAa msuLFmEs waiter A. Schulze and willie w. Crouch, Bartlesville, Okla., assignors to Phillips Petroleum Company, a corporation of Delaware Application November 20, 1943, Serial No. 511,178

- 1 Claim.

This invention relates to a process for the manufacture of valuable alkyl disulfides of high molecular weight. More specifically the present invention relates to the manufacture of high molecular-weight alkyl disuldes from high boiling olens through the intermediate formation of mercaptans followed by selective oxidation to the corresponding disulde. Even more specifically Y this invention relates to the production of valuable lubricating oil additives, comprising alkyl disulildes of high molecular weight, by an integrated process of manufacture involving the interaction of selected oleiins with hydrogen sulfide to form mercaptans which are subsequently converted to disuldes by means of a novel oxidation system.

An object of this invention is to provide an integrated process for the conversion of selected oleilnic hydrocarbons to high molecular-weight y alkyl disulildes by means of the following sequence of operations: (l) catalytic addition of I-IzS to the oleflns to yield mercaptans; (2) selective oxidation of the mercaptans to the alkyl disulfides.

' Another object of the present invention is to provide forthe catalytic conversion of high-boiling oleilnic feed stocks to the corresponding mercaptan derivative which may be oxidized to disuldes with a. minimum of purication.

A further object of this invention is to provide a novel oxidation procedure operating in coniunction with a mercaptan synthesis step to produce high molecular-weight disulfides.

' A still further object of this invention is to provide a process of manufacture of high molecular-weight alkyl disulfldes having desirable additive properties with respect to lubricating oils.

We have now discovered that alkyl disuldes of high molecular weight can be advantageously manufactured in a continuous process utilizing selected olens and HzS as the starting raw materials and combining these materials under the inuence of catalysts to produce a mercaptancontaining stream which may be directly subjected to oxidation. We have also found that the recovery of unreacted olenic hydrocarbons and/or diiuents is greatly facilitated subsequent to conversion of the mercaptans to disulfides.

A We have further found that the diluent eiect of the non-mercaptan components in the feed feed to ,the oxidation reaction is beneficial as manifested in decreased foaming and in reduction of thelviscosity of the emuent.

A feature of the present invention is the oxidation system employed in the conversion of high molecular-weight tertiary mercaptans to disul- WEIGHT ALKYL fides. Wevare aware of the extensive art dealing with the oxidation of very dilute solutions of mercaptans to disuliides as applied to the sweetening of gasoline, however virtually no infomation is available with respect to the relatively concentrated mercaptans in the molecular weight range of 174 to about 256 or higher. We have found that mercaptan mixtures, comprised almost exclusively of tertiary types and having average molecular weights of about 200 to 260,are very resistant to the milder oxidizing agents which normally would be expected to eiect the conversion to the disulfide state. Ihus, whereas it is' Y known that the lighter mercaptans, such as those found in natural gas and gasoline, undergo an appreciable degree of oxidation to disuldes when contacted with air; the high molecular-weight tertiary mercaptans of this invention undergo substantially no oxidation when agitatedwith Y pure oxygen for several weeks. We have also observed that tertiary mercaptans having an average molecular weight of 210 remain unchanged when treated with a large excess of 30 per cent hydrogen peroxide. This behavior is in decided contrast to the known action of hydrogen peroxide'in converting t-amyl mercaptan to the corresponding sulfonic acid. It is apparent, therefore, that the conventional concepts pertaining to the oxidation susceptibility of mercaptans do not apply to the high molecular-weight mercaptans of this invention.

We have found that application of cupric chloride sweetening reagent to the mercaptans of this process results in a product containing excessive quantities of cuprous mercaptide indicating failure of the normal sweetening reactions. Although some disulfide could be prepared by such a reaction, the rapid failure of the oxidizing solution and the difliculties encountered in purifying the product render the procedure economically unattractive and infeasible.

We have found that whereas the high molecular-weight mercaptans hereinbefore described are not affected by hydrogen peroxide, the corresponding cuprous salts are readily oxidized to disulildes and cupric chloride according to the following equation:

We have further found that the proper combination of the copper chloride and hydrogen peroxide systems when applied simultaneously result in a smooth and substantially complete conversion of high-boiling tertiary mercaptans 3 to disuldes. Thus, the two oxidizing agents, neither of which is adequate alone. mutually com. plement each other to produce a result which represents a distinct advance in the art of oxidation of high molecular-weight mercaptans.

A specific preferred embodiment oi the present invention is illustrated in the accompanying drawing. The oleiln feed may consist of a fraction oi heavy polymer having from 12 to 14 or more carbon atoms per molecule which in some instances may be admixed with an inert hydrocarbon diluent. This oleiln feed is withdrawn from storage tank I through line 2 and is blended with hydrogen sulnde from tank 3 and line 4 prior to entering reactor 5. The reactor charge composition is so adjusted that a molal excess o! hydrogen sulilde prevails. Reactor 5 may comprise a catalyst case filled with a solid adsorbent catalyst, or it may be 'a turbo-mixer or iet contactor type of reactor in the case of liquid catalysts. The reactor eilluent flows by way of line B to stabilizer 'I where the excess hydrogen sulde is taken overhead through line 8 to the hydrogen suliide storage 3. The product stream now free of H28 is taken via line 9 to fractionator I0 where light mercaptans consisting mainly of lower boiling mercaptan compounds are drawn oil' through line II to storage. The kettle product from this operation which now comprises unreacted olefin and mercaptans of high molecular weight is withdrawn from the column through line I2 and is emulsiiied with controlled proportions of hydrogen peroxide from line I3 prior to injection into the oxidation reactor I4. Suitable means are supplied in the 'reactor I4 to maintain intimate dispersion of the oxidizing solution with the incom-` ing mercaptan feed. The oxidizing solution is essentially an aqueous solution o1' cupric chloride together with HC1 added in suflicient amount to keep the solution in the system the same as one of cupric chloride. The cupric chloride solution is fed to reactor I4 via line 25. During the passage of the organic phase through the oxidation zone. the combined action oi cupric ions and hydrogen peroxide eiiect the conversion of the mercaptans to disuliides with substantially no change in composition' of the oxidizing solution other than the diluent effect of water introduced with the peroxide. The hydrogen peroxide and mercaptan are added at such rates that in the continuous operation described the peroxide is entirely consumed es fast as it is added and therefore its concentration never builds up to any substantial extent in the reaction zone. The hydrogen peroxide does not react in the absence of cupric chloride. 'Ihe hydrogen peroxide is converted to water as it is consumed. The emulsion o! the product stream and copper solution is continuously removed from the reactor via line I5 to separator I6 where gravity separation of the product stream and copper solution takes place.

The oxidized organic phase is continuously discharged through line II to vacuum fractionator I8 where unreacted high-boiling olenic hydrocarbons constitute the overhead stream which is returned to olefin storage I through line I9, The product disultides substantially free of mercaptan impurities are withdrawn from the fractionator through line 20.

The oxidation system is maintained at full strength as indicated in the drawing. 'Ihe somewhat dilute copper solution is removed from separator I8 through line 2|. A portion or all of the stream may be diverted to evaporation zone 23 where the solution is concentrated with water vapor being discharged through line 24. The

concentrated solution is recycled to the oxidation v reactor I4 through line 2B along with dilute copper solution from line 2i. make-up copper solution from line 2l and replacement HC1 from line 2l. Addition o! HC1 is necessary because some is lost in the evaporation in unit 23 which tends to cause the cupric chloride solution to become basic preventing operation.

In the mercaptan-synthesis stage of this invention, catalytic reactions are especially desirable since the high molecular weight mercaptans specied before are not sufliciently stable to withstand the high temperatures required in straight thermal processes. The reaction between the oleiins and hydrogen suliide may be effected in the presence of a variety of solid and liquid catalysts. Solid contact catalysts may include: silica promoted with various metal oxides, metallicv suliides, silica gel, iullers earth and charcoal. Liquid catalysts such as sulfuric acid, hydrogen fluoride and various complex compounds of boron uoride may be used to promote the reaction.

A preferred solid contact catalyst is a gel-type material comprised essentially of silica and a metal oxide selected from group 111A or IVB oi the periodic system with variant quantities oi water. Silica-alumina compositions represent speciilc types that may be employed to bring about a high conversion per pass at temperatures ranging from about 200 to about 300 F.

Among available liquid catalysts, anhydrous hydrogen fluoride and complex compounds oi boron fluoride with phosphoric acid and water are preferred due to their high activity at low temperatures. With these catalysts under conditions of liquid-liquid contacting, mercaptan formation can be effected at temperatures ranging from about 32 to about 100 F.

The hydrocarbon feed for the present process is ordinarily coniined to aliphatic oleflns having i'rom about 12 to about 16 carbon atoms per molecule. A convenient source of such material is the heavy polymer produced in catalytic codimer operation charging propylene and butylene.

General reaction conditions employed in the mercaptan stage include: (1) a molal excess oi H28 with respect to olefin of about 1:1 to 1:6; (2) reaction pressures of 500 to about 2000 p. s. i. to maintain liquid or dense phase operation.

'I'he oxidizing copper solution oi the disulfide conversion stage comprises an aqueous solution of cupric copper in the presence of a chloride ion concentration equivalent to that of 10 to 20 weight per cent sodium chloride solution. The cupric copper concentration may vary from about 3 per cent to about 14 weight per cent although intermediate concentrations of from about 5 to l0 per cent are ordinarily preferred.

The hydrogen peroxide of the oxidizing system may vary in concentration from about 3 per cent to 30 per cent aqueous stabilized solutions. However, because of the considerable diluent effect on the copper solution and consequent load on the evaporators of the dilute solutions, the more concentrated reagents containing from l5 to 30 per cent H2O: are preferred. Regardless of the strength of the peroxide solution, it is desirable to have a slight excess of H2O2 over that called for in a hypothetical direct stoichiometric oxidation of the mercaptan to disulfide. Thus 1.1 times the theoretical weight of H2O2 has been found adequate although higher concentrations obviously may be employed.

The volume ratio of copper solution to dry mer captan-containing feed may vary from 2 to about 10. However, because of the diluent effect of the hydrogen peroxide introduced with the charge, this ratio is more often maintained between about 4 and 10. The volume of hydrogen peroxide solution required for the reaction varies with the concentration. Thus, the hydrogen peroxidemercaptan volume ratio may vary from about 0.25 for concentrations close to 30 per cent to about 2.5 for peroxide dilutions as low as 3 per cent. In general, the volume ratio of H2O2 to mercaptan is maintained between about 0.05 and 0.10 and preferably about 0.075.

Under optimum conditions with respect to the oxidation potential of the copper solution and in the presence of hydrogen peroxide, the rate of oxidation of these high molecular-weight mercaptans is too slow to be of practical value at temperatures below about 120 F. However, at temperatures between 120 to 150 F. a smooth reaction occurs in most instances. However, in cases involving highly refractory mercaptans reaction temperatures as high as 200 F. may be necessary.

With the employment of the oxidation of this invention under the conditions previously set forth, reaction times ranging from to 60 minutes may be required. However, we have found that in most instances substantially complete conversion of mercaptans to disulfides is realized with reaction times of from 20 to about 40 minutes.

It has been found that the clear, viscous and high-boiling disulfides produced by this process are suitable for use as lubricating oil additives or for any other use where high molecular-weight organic disulfides of comparable purity may apy ply, such as modifiers in emulsion polymerization of co-monomers, typically butadiene and styrene, to synthetic rubber.

While the invention is set forth in detail in the example previously presented, it is to be understood that many modifications and variations will be obvious and no undue limitations are lntended.

We claim:

The process of preparing high molecular weight alkyl disulfides having the general formula R-S-S-R where R is an alkyl group having from 12 to 16 carbon atoms which comprises reacting a C12 to Cm olen with hydrogen sulfide to form the corresponding alkyl mercaptan, removing unreacted hydrogen sulfide and mercaptans having less than 12 carbon atoms from the reaction mixture, subjecting the resulting reaction mixture containing the Cia to Cie alkyl mercaptan together with unreacted olen to the simultaneous action of hydrogen peroxide and aqueous cupric chloride solution and thereby oxidizing the mercaptan content thereof to said disulfide, the unreacted olen serving to minimize foaming and reduce viscosity during the oxidation, vacuum fractionating the unreacted olefin from said disulfide and recycling said unreacted olefin to said reacting step for further reaction with hydrogen sulfide, and recovering said disulfide as the product of the process.

WALTER A. SCHULZE. WILLIE W. CROUCH.

i REFERENCES CKTED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,150,656 Lounsbury" Mar. 14, 1939 2,052,268 Williams Aug. 25, 1936 2,094,485 Buell Sept. 28, 1937 Re. 20,938 Hoover (l) Dec. 6, 1938 2,042,053 Hoover (2) May 26, 1936 2,297,650 Fry Sept. 29, 1942 OTHER REFERENCES Kalichevsky & Stagner, Chemical Refining of Petroleum, 2nd ed., 1942, Reinhold, New York, N. Y., publishers. 

